Spatial Distribution,Food and Activity of Gomphus pulchellus SELYS 1840 (Insecta; Odonata; Gomphidae) from a Still Water Habitat

Distribution patterns of Gomphus pulchellus larvae in different sediments with different density of prey organisms were studied in the field in a small gravel pit lake in the south of Germany. Larval burrowing behaviour at different temperatures as well as food preference, consumption rates and activity were studied in laboratory experiments. In the study lake G. pulchellus larvae lived exclusively in places where macrophytes were present and in fine sediments (mean grain size <3 mm) with detritus cover. There was a significant positive correlation between larval density and density of food organisms suggesting that abundance of food is one of the determinants of larval distribution. In late autumn larvae migrated to deeper places probably to survive the winter. Low temperatures simulated in laboratory experiments did not induce larvae to burrow deeper. Larvae were always found in a sediment depth of 0.59–0.74 cm. Experiments with mixed prey showed that G. pulchellus larvae preferred tubificid worms and chironomid larvae over gammarids and ephemerid larvae. However, chironomid larvae which stayed in their tubes had a higher survival rate than those outside of tubes. Single-prey experiments showed that G. pulchellus larvae can prey not only on benthic species but also on Daphnia from the open water. Functional-response experiments showed that one G. pulchellus larva consumes a maximum of 2 to 3 tubificid worms or chironomid larvae per day, which corresponds to a maximum biomass (freshweight) of 5 to 30 mg per day. Video recordings of activity showed that G. pulchellus larvae cover long distances of up to 52 m per night on the substrate surface and that activity on the substrate surface started after midnight and ceased before sunrise. Consumption of Zooplankton prey and high activity above the substrate is interpreted as an adaptation of G. pulchellus larvae to the life in still water habitats.     

Random patch dynamics of larval Chironomidae (Diptera) in the bed sediments of a gravel stream

• 1 The larval chironomid community of the sediment surface and the hyporheic inters titial was investigated in two longitudinal transects of an alpine gravel stream between September 1984 and August 1985. Eighty larval species and species groups were identified, most of which belonged to the subfamily Orthocladiinae. Of all larval individuals 51.1% inhabited the first 10cm of the bed sediments, and 93.2% occurred between the surface and 40cm depth.
• 2 The spatial species turnover showed marked variations between horizontally adjacent sampling sites in each of the four sediment depth layers. In both transects the species composition showed a significantly lower turnover in the upper 10cm of the bed sediments than in the deeper layers.
• 3 Spatial community stability showed an oscillating pattern between all sampling sites due to density shifts of larvae between depth layers. Temporal differences in resilience (local stability) were significantly and positively related to changes in the cumulative discharge pattern in the gravel brook, thus indicating the apparent ability of the community to recover quickly following disturbances.
• 4 The five abundant species, Corynoneura lobata, Synorthocladius semivirens, Tvetenia calvescens, Micropsectra atrofasciata and Rheotanytarsus nigricauda, exhibited significant differences in their sediment depth distribution, with density maxima shifting between depth layers. Spatial autocorrelations suggest that these larvae form patches between neighbouring sampling sites with varying sizes and inter-patch distances in each of four sediment layers. A simulation test, in which individuals of each species were randomly permuted between microhabitats of each depth layer separately, indicated that the patches might have arisen by chance.
• 5 To evaluate the significance of observed spatial resource overlap values amongst these five chironomid species, neutral models were developed based on 300 randomizations of each possible species pair-wise association of individuals and patches of species. The spatial organization of a larval chironomid assemblage in the stream Oberer Seebach seemed to be governed by coexistence due to random patch formation and dispersal patterns within the interstitial habitats, which reduce the probability of strong competitive interactions.

     

Carabid populations in field beans and their effect on the population dynamics of Sitona lineatus (L.)

The abundance and diversity of potential carabid predators of Sitona lineatus (L.) in field beans were monitored between 1980 and 1983. The absolute abundance of the large predatory species was determined in mark-recapture experiments and a radio-labelling technique was used to estimate the level of predation in the field. Using previously published population data for S. lineatus, the importance of predation in the population dynamics of the weevil was estimated. The mortality of weevil larvae due to predation varied from 0.6%– 10.5% while that of adult weevils varied from 2.6%– 23.8%. It appeared that carabids played a significant role in the population dynamics of S. lineatus and, in years when abundant, could reduce the population of larvae and overwintering adults by more than 30%.     

Temporal and spatial distribution of chironomid larvae and oligochaetes in two Dutch storage reservoirs

Long-term changes in distribution and taxonomic composition of chironomid larvae and oligochaetes in two water storage reservoirs in The Netherlands were studied. A succession among the chironomid species was observed. In the last 10–15 years chironomid densities varied. Compared with other lakes chironomid densities were high. Densities of chironomids were higher in the littoral zone than in the profundal zone. The opposite was found for oligochaetes. Densities and composition of the chironomid fauna in the two reservoirs were similar.Procladius, Tanytarsus andHarnischia dominated at all depths. However, pupal exuviae samples showed some differences in chironomid taxonomic composition between the two reservoirs. Orthocladiinae, rarely found in bottom samples, abounded in pupal exuviae samples.     

Pelagic food web interactions among benthic invertebrates and trout in mountain lakes

1. Benthic chironomid larvae and the amphipod Gammarus lacustris have been observed in the pelagic habitats of many mountain lakes. The main goal of this study was to determine if chironomid larvae and gammarids potentially affect predator–prey and nutrient dynamics in pelagic food webs of mountain lakes. 2. Eighty‐six mountain lakes were surveyed in Alberta and eastern British Columbia during the years 1965–1984, 1991–2004 and 2005–2007. Pelagic chironomid larvae were found in 86% of these lakes, and pelagic gammarids were found in 29% of lakes. Densities of pelagic chironomid larvae were 92% lower in lakes with pelagic gammarids and 76% lower in lakes with trout (P < 0.05). Intraguild predation of trout on gammarids appeared to reduce predation pressure on chironomid larvae. Gammarids consumed in vitro about 1 chironomid per gammarid per day or about 20% of their body mass in chironomid biomass per day. 3. Concentrations of total dissolved P and N, particulate C, and chlorophyll‐a increased with increasing densities of pelagic gammarids and chironomid larvae in situ (R² = 0.14 ± 0.19 SD, P < 0.1) and in vitro (P < 0.001). 4. Our findings suggest that gammarids and chironomid larvae are linked as predators and prey in pelagic food webs, possibly stimulating phytoplankton abundance via nutrient release.     

Relationship between δ13C of chironomid remains and methane flux in Swedish lakes

1. Methanogenic carbon can be incorporated by methane‐oxidising bacteria, leading to a ¹³C‐depleted stable carbon isotopic composition (δ¹³C) of chironomids that feed on these microorganisms. This has been shown for the chironomid tribe Chironomini, but very little information is available about the δ¹³C of other abundant chironomid groups and the relationship between chironomid δ¹³C and methane production in lakes. 2. Methane flux was measured at the water surface of seven lakes in Sweden. Furthermore, fluxes from the sediments to the water column were measured in transects in two of the lakes. Methane fluxes were then compared with δ¹³C of chitinous chironomid remains isolated from the lake surface sediments. Several different chironomid groups were examined (Chironomini, Orthocladiinae, Tanypodinae and Tanytarsini). 3. Remains of Orthocladiinae in the seven study lakes had the highest δ¹³C values (?31.3 to ?27.0‰), most likely reflecting δ¹³C of algae and other plant‐derived organic matter. Remains of Chironomini and Tanypodinae had lower δ¹³C values (?33.2 to ?27.6‰ and ?33.6 to ?28.0‰, respectively). A significant negative correlation was observed between methane fluxes at the lake surface and δ¹³C of Chironomini (r = ?0.90, P = 0.006). Methane release from the sediments was also negatively correlated with δ¹³C of Chironomini (r = ?0.67, P = 0.025) in the transect samples obtained from two of the lakes. The remains of other chironomid taxa were only weakly or not correlated with methane fluxes measured in our study lakes (P > 0.05). 4. Selective incorporation of methane‐derived carbon can explain the observed correlations between methane fluxes and δ¹³C values of Chironomini. Remains of this group might therefore have the potential to provide information about past changes in methane availability in lakes using sediment records. However, differences in productivity, algal δ¹³C composition and the importance of allochthonous organic matter input between the studied lakes may also have influenced Chironomini δ¹³C. More detailed studies with a higher number of analysed samples and detailed measurement of δ¹³C of different ecosystem components (e.g. methane, dissolved inorganic carbon) will be necessary to further resolve the relative contribution of different carbon sources to δ¹³C of chironomid remains.     

INFECTION OF AEDES AEGYPTI LARVAE BY AXENIC CULTURES OF THE FUNGAL GENUS SMITTIUM (TRICHOMYCETES)

Spores from axenic cultures of Smittium spp., isolated from various geographical locations and from different dipteran hosts (mosquito, black fly, and chironomid larvae), were fed to mosquito larvae (Aedes aegypti). We were able to demonstrate some host specificity at the insect family level, but no significant differences in infectivity by isolates from different geographical areas. Spore germination and thallus attachment were observed in the host hindgut within 1.5 hr post spore ingestion. Preliminary studies indicate that S. culisetae has little effect on A. aegypti larvae when they are reared under conditions that promote pupation within 5–6 days. However, ingestion of large numbers of spores by 1st instar larvae growing under suboptimal nutritional conditions may produce fungal growth detrimental to larvae.     

Seasonal changes in the stable isotope values of lake-dwelling chironomid larvae in relation to feeding and life cycle variability

1. We studied seasonal changes in the carbon and nitrogen stable isotope ratios of larval Chironomus anthracinus and C. plumosus from the profundal sediments of four contrasting lakes. 2. Pronounced seasonal changes in both δ¹³C and δ¹⁵N values were evident in chironomid larvae of both species from two summer‐stratified, eutrophic lakes: Esthwaite Water and Wyresdale Park. Changes were most marked in the larvae of C. plumosus and in larvae from greater depths. In contrast, neither C. anthracinus in summer‐stratified but mesotrophic Schöhsee, nor C. plumosus in polymictic Großer Binnensee, showed marked seasonality in larval stable isotope ratios. 3. The particularly strong ¹³C‐depletion of larvae from the stratified, eutrophic lakes is attributed to a significant contribution of methane‐derived carbon to their diets. Feeding by larvae on isotopically light methanotrophic bacteria appears to occur mainly when autumn overturn of the water column restores oxygenated conditions to the sediment surface. At this time both δ¹³C and δ¹⁵N values of larvae decreased sharply. 4. Changes in the mean stable isotope ratio of the larval populations can also occur when larger, more isotopically light, larvae pupate and emigrate from the population to hatch as imagos. This effect can induce seasonal changes in larval isotope values even in lakes in which there is no evidence of a significant involvement of methane‐derived carbon in their diets. Variations in emergence patterns between species and between lakes may generate differences in the seasonal pattern of change in stable isotope ratios in larval populations. 5. Our results emphasise the importance of adequate seasonal sampling if stable isotope ratios are to be used as biomarkers to study the role of key groups, such as chironomid larvae, in the trophic structure of lakes.     

Subfossil chironomid assemblages in deep,stratified European lakes: relationships with temperature,trophic state and oxygen

1. The distributions of subfossil remains of chironomid larvae in 28 large, deep and stratified lakes in Europe were examined in surface sediments along a latitudinal transect ranging from northern Sweden to southern Italy. 2. Canonical correspondence analysis (CCA) showed that summer surface water and July air temperature, as well as total phosphorus (TP) concentrations, hypolimnetic oxygen availability and conductivity were statistically significant (P < 0.05) explanatory variables explaining between 11 and 14% of the variance in the chironomid data. 3. Owing to the spatial scale covered by our study, many environmental variables were covarying. Temperature, TP concentration and oxygen availability were positively or negatively correlated with the first axis of a detrended correspondence analysis (DCA) of chironomid assemblages, suggesting that climatic and trophic conditions influenced profundal chironomid assemblages either in a direct (food and oxygen) or in an indirect (temperature) way. Parameters related to local environmental conditions, lake morphology and bedrock geology, such as organic matter content of the sediment, maximum lake depth, Secchi depth and pH, were not significant in explaining the distribution of chironomid assemblages in our study lakes. 4. The strong relationship between chironomid assemblages and summer temperature may be related to the covariation of temperature with parameters, such as nutrient and oxygen availability, known to affect chironomid assemblages in deep, stratified lakes. However, summer temperature explained a statistically significant proportion of the variance in the chironomid assemblages even when effects of oxygen availability and TP concentrations were partialled out. This suggests that summer temperature has an effect on chironomid assemblages in deep lakes, which is not related to its covariation with trophic state. 5. The potential of fossil chironomid analysis for quantitatively reconstructing past nutrient conditions in deep, stratified lakes was examined by calculating the Benthic Quality Index (BQI) based on subfossil chironomids and by comparing BQI values with observed TP concentrations. BQI was linearly related to log‐transformed TP. Applying this relationship to fossil chironomid assemblages from Lake Päijänne (Finland) produced a TP reconstruction in agreement with measured TP during the period 1970–1990, demonstrating that this approach can provide quantitative estimates of past nutrient concentrations in deep, stratified lakes.     

The effect of a predatory leech,Nephelopsis obscura,on mortality,growth, and production of chironomid larvae in a small pond

Summary The effect of a predatory leech, Nephelopsis obscura, on survivorship, growth, and production of chronomid larvae was studied by enclosure experiments carried out in a small pond. The prey population was composed almost entirely of the tubiculous, microphagous chironomid larvae, Chironomus riparius and Glyptotendipes paripes. Nephelopsis significantly reduced chironomid survivorship within the enclosures, and accounted for most of the measured mortality of fourth instar larvae. The cropping by Nephelopsis was not significantly biased toward either prey species. In long-term experiments (66 d) chironomid biomass in enclosures without leeches reached much higher levels than in enclosures containing Nephelopsis. This increase in biomass was due to growth of surviving larvae, rather than recruitment, since emergence and oviposition were not going on during the course of the experiments. The enhanced survivorship of larvae within leech-free enclosures was eventually accompanied by reduced growth and specific production (daily production/biomass) for C. riparius, which made up about 90% of the larval population. Growth and specific production of G. paripes (10% of larval population) was not affected. Short-term experiments (25 d) involving manipulation of densities and species ratio (9:1 CR:GP and 1:9 CR:GP) of larvae revealed that growth of the majority species was strongly influenced by larval density, whereas growth of the minority species was not. The same pattern was observed both in the presence and in the absence of Nephelopsis and was a result of differences in resource utilization between the two species. In the shortterm experiments, growth rates estimated for larvae exposed to leeches were significantly less than those for larvae in leech-free enclosures. This could be due either to size-biased consumption of larvae by Nephelopsis, or possibly a disturbance factor leading to reduced larval food intake and/or increased metabolic costs.     

Survival of Salmonella enterica in Freshwater and Sediments and Transmission by the Aquatic Midge Chironomus tentans (Chironomidae: Diptera)

Survival of a nalidixic acid-resistant strain of Salmonella enterica serovar Typhimurium mr-DT-104 in water and sediments was tested using artificially contaminated aquaria. Water samples remained culture positive for salmonella for up to 54 days. Sediment samples were culture positive up to 119 days. In addition, potential mechanisms for spreading salmonella in the environments by chironomid larvae and adults were tested. We evaluated the acquisition of mr-DT-104 by chironomids from contaminated aquatic sediments and subsequent spread to uncontaminated sediments. Larval chironomids raised in contaminated sediments became culture positive, and the bacteria were carried over to adults after emergence. Contamination of clean sediments by chironomid larvae was not demonstrated. These findings clearly suggest that mr-DT-104 serovar organisms can survive in aquatic sediments for at least several months. Uptake of salmonellae by chironomid larvae and adults suggests that they are possible vectors of mr-DT-104 in both aquatic and terrestrial environments, although the role of larval defecation in movement of bacteria to new sediments was not demonstrated.     

Instar distribution and biomass of Chironomidae larvae in Lago El Junco, Isla San Cristobal, the Galápagos

The distribution, abundance and standing crop biomass of chironomid larvae were determined at one-meter depth intervals along three radial transects. Samples were collected by coring soft sediments while diving. Three genera were found in the lake: Chironomus sp. (collector-filtering larvae), Ablabesmyia sp. (predatory larvae) and Goeldichironomus sp. (collector-filtering larvae). Standing crop densities of chironomids, averaged over the entire lake, varied from 30,594 larvae/m² to 11,428 larvae/m² at different depths. No statistically significant zonation in density was found for the two most common taxa, Chironomus sp. (87.8% of specimens) and Ablabesmyia sp. (9.0%), however the deepest zones (>4 m) had the lowest estimated densities. Significant differences in standing crop biomass were detected, with the 6 m depth having greatest biomass. The increase in standing crop biomass was a function of (1) lower frequency of first instars of Chironomus sp. and Ablabesmyia sp. at 6 m (2) higher average larval biomass of both species at 6 m and (3) very significant increase in average biomass of fourth instars of Chironomus sp. at 6 m compared to fourth instars at shallower depths. These results indicate that the lentic chironomids of this isolated oceanic habitat consist of a small number of species that are ecological generalists and tolerant of low oxygen concentrations.     

The effect of tubificids and chironomids on particle redistribution of lake sediment

The effects of chironomid larvae,Chironomus plumosus, and tubificid worms,Limnodrilus spp., on particle redistribution in lake sediment were investigated experimentally using pots containing sediments obtained from Lake Suwa, Japan. The chironomids and tubificids increased the water content of surface sediment. The chironomid larvae had no effect on particle size distribution, while tubificids continuously accumulated small particles on the surface sediment through their selective feeding activity. Particles larger than 0.125 mm were buried at a sediment depth of 6 cm. In Lake Suwa, long diatom frustules, large plant debris and blue-green algal flocs were found to accumulate in the deeper layer of the lake sediment inhabited by tubificids at high density.     

Veligers of an introduced bivalve,Limnoperna fortunei,are a new food resource that enhances growth of larval fish in the Paraná River (South America)

1. Larvae of ‘sábalo’, Prochilodus lineatus, whose adults represent over 60% of overall fish biomass in the Río de la Plata Catchment, have been observed to feed intensively on veligers of the exotic bivalve Limnoperna fortunei. 2. To assess the effects of this dietary shift on the growth of P. lineatus, 28‐day laboratory experiments were carried out feeding newly hatched P. lineatus larvae with three diets: zooplankton artificially enriched with L. fortunei veligers; natural zooplankton; and zooplankton artificially enriched with cladocerans and copepods. The average length, weight and gut contents of the fish larvae were assessed weekly and metabolic rates of fish larvae were measured. 3. Proportions of veligers in gut contents were always higher than those in the experimental diet: 100, 76 and 21% for veliger‐enriched, natural and low‐veliger diets, respectively. Larvae fed a veliger‐enriched diet grew to a significantly larger size than larvae fed the other two diets. In energetic balance comparisons using metabolic rates and prey energy content, all three diets were sufficient to support metabolism and growth. The greatest values of excess energy at the end of each week were in the veliger‐enriched experiments. 4. Feeding on veligers of L. fortunei significantly enhances the growth of P. lineatus larvae and supports the idea that this new and abundant resource is selectively preyed upon by P. lineatus during its larval stage. Higher growth rates may stem from the higher energy contents of veligers compared to crustaceans and/or from the lower energy costs of capturing slower prey.     

Influence of Chironomidae (Diptera) faecal pellet accumulation on lake sediment quality and larval abundance of pestiferous midge Glyptotendipes paripes

Two opposite distribution patterns of larval Glyptotendipes paripes in relation to organic carbon content in sediments of central Florida lakes were discovered. In a majority of examined lakes, G. paripes larvae were most abundant in sand sediment and their density rapidly declined with increased carbon content (type 1 lakes); however, in some cases the opposite was true (type 2 lakes). To elucidate this anomaly, field-collected organic sediments from types 1 and 2 lakes and sand sediment were studied for G. paripes development in the laboratory. Type 1 organic sediment consisted predominantly of fine particles (<0.25 mm diameter) with low dissolved oxygen levels, whereas type 2 organic sediments consisted primarily of chironomid large faecal pellet aggregates (>0.25 mm diameter), with significantly higher levels of dissolved oxygen concentrations that were similar to sand sediment. Type 2 organic sediment and sand sediment were conducive to higher survival of G. paripes larvae than fine organic sediment. The larvae in type 2 organic sediment produced longer tubes than in other sediment types. This observation indicates that accumulation of chironomid faecal pellets in lake sediments may change physical properties, such as dissolved oxygen level and consequently alter conditions for survival of chironomid larvae and possibly other benthic fauna.     

Interactions ofMonoporeia affinis (Lindström) (Amphipoda) with sedentary Chironomidae

Interannual population oscillations ofMonoporeia affinis and sedentary chironomids are negatively correlated in Lake Mälaren. Sedentary chironomid abundance regressed againstM. affinis density was highly significant at a lag response of one year (adj. R²=0.54, P=0.0001). The inverse correlation between Tanytarsini (Micropsectra sp. andTanytarsus sp.) andM. affinis densities supports a recruitment limitation hypothesis,viz. that the growth or survival of early instar chironomids is low at high amphipod densities. Microcosm studies showed density-dependent effects on the growth and survival of second instarCh. riparius larvae across an amphipod density gradient. No significant effects were found on growth or survival of third instars. These findings support the chironomid recruitment limitation hypothesis. Amphipod predation on early instar chironomid larvae is suggested as a population controlling mechanism.     

A preliminary health risk assessment of heavy metals in local and imported rice grains marketed in Trinidad and Tobago,W.I.

Abstract

Within recent times, heavy metal contamination in rice (Oryza Sativa) has been of growing concern particularly due to its implications on human health via consumption. Twenty-one different brands of rice marketed in Trinidad and Tobago were investigated for their heavy metal content (Cd, Cr, Cu, Mn, Ni, Pb and Zn) using Flame Atomic Absorption Spectroscopy. Lead was not detected in any of the samples, while both Cadmium and Nickel were detected in only one sample each at 0.27 and 1.79?µg/g, respectively. The average metal concentrations decreased in the following order: Zinc?> Manganese?> Copper?>?Chromium with concentrations ranging from 1.00–4.35, 1.72–29.92, 5.87–43.56 and 0.06–1.16?µg/g, respectively. The target hazard quotient (THQ) and hazard index (HI) values for all samples were less than one, indicating no risk of non-carcinogenic effects to consumers.     

Effects of bioturbation by tube-dwelling chironomid larvae on oxygen uptake and denitrification in eutrophic lake sediments

1. Oxygen uptake and denitrification were determined in two bioturbated sediments from a eutrophic lake in southern Sweden. In laboratory mesocosms, an organic profundal sediment was incubated with Chironomus plumosus L. and a sandy littoral sediment with an organic-rich top layer was incubated with Polypedilum sp. Both species of chironomid are sediment tube-dwelling. 2. Oxygen consumption, expressed per gram of larval dry weight, was enhanced to the same extent by the larvae in both sediments. Measurements of the respiration rate of individual larvae revealed that the respiration per gram dry weight of the smaller Polypedilum sp. was more than three times higher than that of C. plumosus. 3. Denitrification was measured using the ‘nitrogen isotope pairing’ technique. In the organic sediment, denitrification of nitrate from the water phase (dw) and denitrification of nitrate from coupled nitrification (dn) were each correlated with the biomass of C. plumosus. In the sandy sediment, dw was correlated with the biomass of Polypedilum sp., while dn did not show any correlation with Polypedilum sp. 4. Oxygen uptake in the organic sediment was increased by a factor of 2.5, dw 5-fold and dn 2.5-fold at a biomass of 10 g m^–2 dry weight of C. plumosus. The same biomass of Polypedilum sp. in the sandy sediment resulted in a 2-fold stimulation of oxygen uptake and a 3-fold stimulation of dw, while dn was not affected. These differences in stimulation between oxygen uptake and denitrification by the larvae in the sediments suggest that the stimulation pattern cannot be explained by simple extension of the sediment surface. The burrows evidently reduce the distance between the nitrate source in the water column and the denitrifiers in the anoxic zones. 5. This study indicates that bioturbation by macrofauna elements can have a great impact on denitrification in lake sediments, and that different organisms can influence nitrogen turnover in specific ways.     

The influence of chironomus plumosus larvae on the exchange of dissolved substances between sediment and water

4th instar Chironomus plumosus larvae (about 1000·m^–2) were added to tubes containing sediment and overlying water. At a temperature of 20°C the larvae greatly increased the trasnport of silica, phosphorus and iron from the sediment to the water. Oxygen concentrations did not influence the exchange of silica. For two non-calcareous sediments the exchange of phosphorus and iron was much higher under anaerobic than under aerobic conditions while the difference was small for sediment from a hardwater lake. Exchange of inorganic nitrogen was little influenced by added chironomid larvae.     

Effect of supplementation of a dry feed with natural food on growth, condition and size distribution of juvenile tench Tinca tinca (L.)

In a 120‐day experiment, tench Tinca tinca juveniles [initially, 135 days post‐hatch, 37.4 mm total length (TL), 0.51 g body weight (BW)] maintained at 28°C received commercial starter alone (control group) or together with a supplement of frozen fly or chironomid larvae, in single or double quantities. Final survival rates were 100% in all treatment groups. Double additives significantly (P ≤ 0.05) improved fish growth in TL (final growth 62.0 or 62.5 mm, respectively) as compared with those fed single quantities (both 60.8 mm) or starter alone (59.1 mm). Significant differences in BW were found only between groups fed double additives and starter alone (final growth 2.96–3.07 and 2.71 g, respectively). Significantly highest Fulton's coefficient values were found in the control group and in the group fed single supplement of fly larvae (both K = 1.22), and lowest in both groups receiving chironomid larvae (K = 1.15–1.17). BW distribution was positively asymmetric in all groups, and the distribution of TL only in the control group and in the group fed with the single supplement of chironomid larvae. From a practical point of view, supplementation of a commercial starter with insect larvae has a minor effect on the results of T. tinca rearing under controlled conditions.